90 lines
2.2 KiB
Python
90 lines
2.2 KiB
Python
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from .abc import DefaultMapping
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class _DefaultSize(object):
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def __getitem__(self, _):
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return 1
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def __setitem__(self, _, value):
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assert value == 1
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def pop(self, _):
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return 1
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class Cache(DefaultMapping):
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"""Mutable mapping to serve as a simple cache or cache base class."""
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__size = _DefaultSize()
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def __init__(self, maxsize, getsizeof=None):
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if getsizeof:
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self.getsizeof = getsizeof
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if self.getsizeof is not Cache.getsizeof:
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self.__size = dict()
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self.__data = dict()
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self.__currsize = 0
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self.__maxsize = maxsize
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def __repr__(self):
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return '%s(%r, maxsize=%r, currsize=%r)' % (
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self.__class__.__name__,
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list(self.__data.items()),
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self.__maxsize,
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self.__currsize,
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)
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def __getitem__(self, key):
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try:
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return self.__data[key]
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except KeyError:
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return self.__missing__(key)
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def __setitem__(self, key, value):
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maxsize = self.__maxsize
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size = self.getsizeof(value)
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if size > maxsize:
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raise ValueError('value too large')
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if key not in self.__data or self.__size[key] < size:
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while self.__currsize + size > maxsize:
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self.popitem()
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if key in self.__data:
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diffsize = size - self.__size[key]
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else:
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diffsize = size
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self.__data[key] = value
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self.__size[key] = size
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self.__currsize += diffsize
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def __delitem__(self, key):
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size = self.__size.pop(key)
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del self.__data[key]
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self.__currsize -= size
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def __contains__(self, key):
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return key in self.__data
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def __missing__(self, key):
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raise KeyError(key)
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def __iter__(self):
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return iter(self.__data)
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def __len__(self):
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return len(self.__data)
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@property
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def maxsize(self):
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"""The maximum size of the cache."""
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return self.__maxsize
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@property
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def currsize(self):
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"""The current size of the cache."""
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return self.__currsize
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@staticmethod
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def getsizeof(value):
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"""Return the size of a cache element's value."""
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return 1
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